Transformer responding to variations in amplitude of input waves



P 1949- w. B. CALLAWAY 2,431,644.

TRANSFORMER RESPONDING T0 VARIATIONS IN- AMPLITUDE OF INPUT WAVES FiledJuly 10, 1947 OUTPUT PATH INPUT TYPICAL OUTPUT FIG. 2

FIG.

A A c? INPU T PA TH J FIG. 3

INVENIUR 1 8}) W B. CALL/WAY Paulina Sept. 13, 1949 TRANSFORMERRESPONDING TO VARIA- TIONS IN AMPLITUDE OF INPUTWAVES William B.Callaway, Orange, N. 3., asslgnor to Bell Telephone Laboratories,Incorporated, New York, N. Y., a corporation of New York ApplicationJuly 10, 1947, Serial No. 759,986

.6 Claims. ((1323-48) plitude of the envelope of an alternating voltagewave impressed on its input circuit. The transformer circuit of thepresent invention is an en- 7 velope difl'erentiator transformercircuit.

There are presently known and available in the art circuits whichrespond to variations in the amplitude of the envelope of a voltage waveby generating voltage waves indicative of the change.

The circuit of the presentinvention, however, has the advantage that itis much less expensive than the known circuits.

This circuit may be used, for instance, in communication to identifydial pulses. Such pulses may be generated in dialing, for instance, bychanging the impedance of a line to which an alternating currentvoltage, or tone, of constant amplitude is applied. The variation in theimpedance introduced by the dialing will change the amplitude of thetone voltage wave impressed on the input of the transformer circuit, inaccordance with the pattern of the dial impulses. The change in theamplitude of the wave envelope, correspondingto the signal train of thedial pulses,

impressed on the input circuit will generate a train of voltage waves inthe transformer output circuit indicative of the dialed impulses. Thetransformer circuit of the invention has other applications and may beapplied wherever it is desired to transform a variation in the amplitudeof the envelope of a voltage wave into a signal. Such signal may be ofdiffering patterns and of differing durations dependent upon theconstants of the cooperating apparatus elements in the circuit.

An object of this invention is the transformation of changes inamplitude only of the envelope of a voltage wave in the input of atransformer circuit into voltage waves in the transformer outputcircuit.

Another object of the invention is the control of the duration of thesignal generated in the output circuit in response to the changes in theamplitude of the envelope of the input signal.

A further object of the invention is to provide a less expensive circuitfor indicating changes in corporated. It is to be understood, however,that the invention may be incorporated in other embodiments which willbe comprehended by those skilled in the art from the disclosure herein.In the drawings, Fig. 1 show the transformer circuit of the invention;Fig. 2 shows a typical input wave; and Fig. 3 shows a typical outputwave.

Refer to Fig. 1 which shows the envelope differentiator transformercircuit. The circuit consists of a pair of wires comprising an inputpath connecting to the matched windings A and B of transformer T.Windings A and B are connected in series aiding. These windings aremounted preferably upon an easily saturable magnetic core M, but theinvention may be practiced with any magnetic core. Also mounted uponthis core, and thus electromagnetically coupled to windings A and B, arematched windings C and D. Windings C and D are connected together inseries opposing. These are connected to a pair of wires comprising theoutput path of the device.

Rectifier F is bridged across the input path to transformer T. Theoutput of this rectifier connects to a balanced circuit consisting ofseries resistors RI and R2, a parallel condenser Ci, series condensersC2 and 03, series resistors R3 and R4, and winding E of transformer T.Winding E is mounted on transformer core M upon a magnetic "brldginglink as indicated. Though none is indicated on the drawing, an amplifiermay be included in the circuits associated with the rectifier if this isdesirable for providing either electrical amplification or impedancematching.

Operation of the device is as follows: If an alternating current signalis applied to the input side of the device, essentially no signal will,at first, be transmitted to the output side, due to the fact that thewindings A, B, C and D are so electrically and magneticallyinterconnected that voltages induced in the output circuit areeffectively cancelled. This is true even though the intensity of theinput signal is great enough to saturate the magnetic core on currentpeaks. However, immediately after the input signal is applied, a portionof the input current is rectified by rectifier F and the resultantpulsating direct current is sent into condenser Cl via series resistorsRI and R2. The combination RI, R2 and Cl acts as a filter to essentiallysmooth out the pulsations. The resultant direct current flows to chargecondensers C2 and C3 in series with winding E. The charging current toC2 and to C3, flowing in transformer winding E. creates a magnetizingforce which unbalances the core of transformer T with respect towindings A, B, C

' 3 and D. The magnetic loop linking A and C now saturates at adifferent point in the incoming alternating current signal cycle thandoes that linking windings B and D. As a result, there is a shortperiod, occurring twice in each half-wave of the input signal, duringwhich voltages induced in windings C and D are no longer equal. Hence,these Voltages do not completely cancel out. As a result, whenever thereis charging current in winding E, and an input signal is present.

there is an output signal.

If the envelope of the alternating current signal is constant, thevoltage output of rectifier F is constant. Accordingly, after a timedetermined by the constants of the system, condensers Ci, C2 and C3become essentially fully charged and current no longer fiows in windingE. Thus, the magnetic unbalance disappears. The transformer is againbalanced and no ouput signal is obtained. Now, if the input signal ischanged in amplitude, the voltage out of rectifier F suifers acorresponding change. Accordingly, condensers CI, C2 and C3 start tovary their charge in accordance with this changed voltage, current flowsin winding E, the transformer becomes unbalanced, and an output signalis obtained.

Eventually, the charge on these condensers would reach a new steadystate condition and the output signal would disappear. However, if thechange in intensity of the input signal persists for a short time ascompared to the charging and discharging time of the circuit associatedwith winding E, an output signal will be obtained for the duration ofthe signal intensity change. Following resumption of the normal signallevel, there is a short interval during which winding Es circuit returnsto the original steady state condition. During this time, there will bea signal in the output of the transformer T until the original charge isagain restored to Cl, C2 and C3. The phase of the latter signal is 180degrees removed from the phase of the signal obtained during the shortinterval of envelope change.

It should be apparent that the duration of the signals in the output maybe varied by a proper choice of constants of the charging circuit ofwinding E. Condensers C3, C4 and resistances R3 and R4 may be variableas indicated to vary the duration of the output signals.

Instead of a single core having a bridging path it is obvious that theinvention may be practised with cores of other conformations, such as bymeans of two individual square or rectangular cores each havingindividual central openings and abutting along an edge or by means oftwo separable circular or elliptical rings or tori for instance abuttingalong their outer boundaries.

The input and output signals are indicated in Figs. 2 and 3,respectively.

Fig. 2 shows the voltage wave envelope of a train of signals such asmight be. applied to the input of Fig. 1 by the operation of a dialcircuit which increased the impedance for each dial pulse as seen by anapplied tone.

Fig. 3 shows the resultant output signals. The lengthened first elementof the output train in Fig. 3 results from the lengthened interval ofcurrent flow in the charging circuit of winding E when voltage is firstapplied.

The input is presumed to decrease momentarily to provide an outputsignal. However, it is apparent that the device will operate as well onmomentary increases of signal, provided the circuit constants governingthe charge and discharge of Cl, C2 and C3 are suitable.

We have, thus, a circuit which responds essen- .tially to changes in theintensity of an applied tone. That is to say, it is a dii'ierentiatorcircuit" which acts upon the envelope of the input signal.

What is claimed is:

1. A voltage wave envelope diiferentiator circuit comprising a pluralityof windings on a magnetic core and instrumentalities for producing amagnetic bias in said core in response to variations in the amplitude ofthe envelope of a voltage wave, said instrumentalities comprising awinding on said core and a condenser in series with said winding.

2. A transformer, an input and an output circuit connected thereto, saidcircuits having windings so connected that when the envelope of analternating voltage wave impressed on said input circuit remainssubstantially constant in amplitude, there is substantially no voltageimpressed on saidoutput circuit, and magnetic means in said transformeractuable solely in response to variations in the envelope of saidvoltage wave impressed on said input circuit to produce a voltage insaid output circuit.

3. A transformer circuit comprising an easily saturable magnetic core, afirst winding on said core, a condenser charging circuit connected tosaid winding, input and output windings on said core, magnetic paths insaid core saturable at different points .on a voltage wave impressed onsaid input windings as a result of an unbalance in said paths producedby said first winding in response to changes in the amplitude of anincoming voltage wave, said output windings disposed so as to generatean output wave in response to said unbalance.

4. A voltage wave envelope differentiator circuit, said circuitcomprising a magnetic core, said core easily saturable, said core havingtwo magnetic paths, a first pair of input windings connected in seriesaiding on said core, one of said first pair in each of said paths, asecond pair of output windings connected in series opposition on saidcore, one of said second pair in each of said paths, said windingsdisposed in relation to said paths so that there is no output from saidcircuit when a continuous voltage wave applied to said input is ofconstant amplitude, a control circuit comprising a rectifier, acondenser charging circuit and another winding all interconnectedbetween said input circuit and said core, said other winding wound on abridging path on said core common to said two paths, said controlcircuit responsive to a change in amplitude of said wave to unbalancesaid paths with respect to said input and output windings and impress avoltage wave on said output in response to a change in amplitude of saidinput wave.

5. A circuit in accordance with claim 4 including means for varying theduration of the output signals.

6. A voltage wave envelope diiferentiator circuit comprising twomagnetic cores having a common magnetic link, a biasing windingencircling a portion of said link, an individual input winding on eachof said cores, an individual output winding on each of said cores, saidwind-.

ings so arranged that there is substantially no voltage impressed acrossa circuit connected to said output windings when an alternating voltagewave of substantially constant amplitude is impressed across an inputcircuit connected to said input windings, means responsive to avariation in the amplitude of an input voltage wave .6 impressed on saidinput windings for biasing said UNITED STATES PATENTS cores through saidbiasing winding, and means responsive to said biasing for producing anout- Number Name Date put voltage wave in said output windings indica-1,374,240 Case 1932 tive of said variation. 5 3 L Lee J e 2 1944 eWILLIAM B. CALLAWAY.

REFERENCES CITED The following references are of record in the file ofthis patent:

